Scoitish Ai'5o7''ic7iltural Society. 565 



doing in the great forests of Germany, in working out the problem of the 

 Influence of forests on climate. As some of them would be aw.ire, meteoro- 

 logical observations were carried out there of a very elaborate character. 

 At each forest station three distinct positions were iixed upon. In the 

 centre of an open field, covered with grass, two or three hundred yards 

 from the forest itself, so as to be perfectly uninfluenced by the trees, ther- 

 mometers were placed down. Then thermometers were placed at the top 

 of a tree in the heart of the forest ; and again at the foot of a tree, where 

 they were screened from sun and light. Underground thermometers 

 were also placed down, and the whole of these were observed several times 

 a day. Looking at the results obtained after several years of observation, 

 he found that, taking the mean temperatures in the open spaces outside, 

 and comparing them with the temperatures near the top of the tree, they 

 had all l)ut identity. There were differences between the temperatures on 

 the grass at the surface of the earth and at the top of the trees at certain 

 hours of the day, but he spoke simply of mean results. Comparing the 

 thermometer at the top of the tree with that at its foot, they had, however, 

 a very great difference, the temperature being considerably lower under the 

 trees than at the top or outside the wood. Looking at the underground 

 temperatures, it was found that the temperature of the soil shaded from 

 the sun by the trees in the heart of the wood varied from two to four de- 

 grees below the mean of outside of the wood under a full exposure of 

 the sun but protected by the grass. At the society's station at Carnwath 

 it was impossible to carry out the experiments so fully, owing to the want 

 of observers and of elaborate sets of instruments. It was resolved that 

 the step they should take at Carnwath would be to attempt to throw 

 further Hght upon this question, viz., What effect had trees in modifying 

 the temperature of the air around them, and the temperature of the soil in 

 which they grew ? and it was to that question that the committee should 

 give attention for some time to come. It was so important, and it opened 

 up so many practical questions, that he thought the effort should be made. 

 At Carnwath the society had two sets of apparatus— one fully exposed to 

 the sun's light and heat, and the other quite near, but completely sheltered 

 from the sun. Besides those on the surface, underground thermometers 

 were sunk at a depth of three, twelve, and twenty-two inches. Since 8th 

 March tiU the end of July observations had been made. Taking the maxi- 

 mum and minimum of thermometers in the open space, they gave a mean 

 temperature from March to July of 46 "6, exactly coinciding with the mean 

 of the dry bulb thermometers. The mean temperature of the thermometers 

 in the boxes inside the wood, and protected by the trees, was 46-1, or 

 exactly half a degree lower. March was the coldest month of the year, 

 and during it the difference between the two was almost nil ; but in 

 summer the difference was much greater. The difference of the tempera- 

 ture on the soil in the two positions was even more marked, being greatest 

 when the sun's strength was greatest. In July the soil in the shady posi- 

 tion, three inches underground, was 3*2 degrees lower than in the open ; 

 at twelve inches, 3'5 degrees lower ; and at twenty-two inches, 3"9 degrees, 

 VOL. I. 2 b 



